Summary of studies using the transgenic rats in 2017: 1. Dopaminergic dysfunction in HIV transgenic rat: We have previously reported significantly decreased D2/3 receptors in the adult Tg rat brains compared to age-matched controls, in both the dorsal striatum (DS) and ventral striatum (VS), using 18F-fallypride PET imaging. In younger animals, the decrease in D2/3 receptors was only significant in the DS, suggesting that there was a continuous trend of neurological/dopaminergic damage that worsens with age. The combination of decreased TH that we saw on immunofluorescence (early step in dopamine synthesis) and decreased post synaptic receptor density (D2/3) seen on PET supported the notion of dopaminergic neuronal dysfunction/loss in this animal model. We concluded that 18F-fallypride can detect dopaminergic system dysfunction in the Tg rats and may be a reasonable imaging biomarker to evaluate neuroprotective approaches. We wanted however to further evaluate the pre-synaptic component of the dopaminergic system using another PET ligand, 18F-FP-CMT. Using two groups of rats (5-8 Month-old and 15-18 Month-old), we found that the 18F-FP-CMT and 18F-Fallypride binding potential (BPND) values were significantly lower in 15-18 month-old Tg compared to age-matched WT rats (p< 0.0001 and 0.001, respectively). 18F-FP-CMT BPND values in 5-8 month-old rats, however, were not significantly different. Longitudinal age-related decrease in 18F-FP-CMT BPND was exacerbated in the Tg rat. We concluded that there is both presynaptic and postsynaptic dopaminergic dysfunction/loss in older Tg compared to WT rats. We believe this to be related to neurotoxicity of viral proteins present in the Tg rats serum and brain. 2. Role of oxidative stress in the neuropathology of the tg rat: HIV-associated neurocognitive disorder (HAND) continues to be a widespread problem, and progression of neurocognitive impairment caused by aging in individuals with HIV has been reported. HAND is characterized by an increase in reactive oxygen (ROS), and reactive nitrogen species (RNS) at the cellular level. Motor and behavioral dysfunction are among the common symptoms and it is believed that oxidative and nitrosative stress contribute to mechanistic changes leading to neurocognitive impairment. Our previous imaging, histological, motor and behavioral assessments support a dysregulation in dopaminergic function as the HIV-1 Tg rat ages. The goal of this study was to demonstrate the presence of oxidative and nitrosative stress within the neuroanatomic areas associated with dopaminergic dysfunction in the HIV-1 transgenic (HIV-1 Tg) rat brain. We found pathology consistent with pre-synaptic dopaminergic neuronal loss, increases in striatal NADPH oxidase-4 (Nox4) and neuronal nitric oxide synthase (nNOS) expression with associated increase in 3-nitrotyrosine (3-NT) modified neurofilament proteins in the basal ganglia neurons of HIV-1 Tg rats compared to age-matched wild type rats. Those abnormalities were seen in the 9 month-old but not in the 3 month-old rats. Finally, this increase in free radical mediated neuronal pathology occurred without significant induction of the transcription factor Nrf2 and redox adaptation of the Nrf2 responsive thioredoxin and glutathione antioxidant system. Our findings suggest that in the aging HIV-1 Tg rat, possibly due to chronic exposure to HIV-1 proteins and lack of appropriate redox adaptation, nitrosative stress and 3-NT modification of neurofilament proteins of basal ganglia neurons is hastened possibly contributing to structural changes to dopaminergic neurons and secondary dopaminergic dysfunction Summary of studies using the SIV infected monkeys: 1. We hypothesized that 11C-DASB binding will be affected in SIV infection (with respect to pre-inoculation scans). We are using rhesus macaques infected with the neurovirulent SIV strain, SIVsm804E. We have finished acquiring PET imaging targeting SERT using 11C-DASB in monkeys before and after inoculation, in order to detect serotonergic system status under the effect of SIV infection. We found that the serotonin transporter (SERT) levels/expression increased in most animals (6 out of 7) that were inoculated with SIV when we compared the last time point imaging (11C-DASB PET) to the preinoculation scans. We are investigating a potential epigenetic effect of the virus on SERT expression at this point and preparing a manuscript. 2. We are also investigating the evolution of neuroinflammatory changes in the SIV-infected monkeys using peripheral viremia and disease control (simulating optimally treated HIV+ patients) as covariants. Towards this goal, we have finished acquiring 18F-DPA-714 PET imaging as biomarker of microglial activation (neuroinflammation), in vivo, in the SIV-infected monkeys. Unlike our expectations, we did not find increased translocator protein expression using 18F-DPA714 PET imaging in the monkeys (5 out 5 showing decreased binding after inoculation rather than increased binding). We believe this correlates to the severity of CNS involvement as measured by CSF viral load. We are now